Nth Prime

Tue, 15 Dec 2020 08:21:32 +0000

Prime number is an age old problem. I am trying to solve it via streams.

class PrimeCalculator {

 public int nth(int nth) {
 if (nth <= 0)
 throw new IllegalArgumentException();

 // Will skip the nth - 1
 // 2 to n-1
 return IntStream.iterate(2, i -> i + 1).filter(PrimeCalculator::isPrime).skip(nth - 1).findFirst().getAsInt();
 }

 public static boolean isPrime(int x) {
 // till half of x
 return IntStream.rangeClosed(2, (int) (x/2) ).dropWhile(i -> x % i != 0).findFirst().isEmpty();
 }
}

Explanation
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public int nth(int nth) {
 if (nth <= 0)
 throw new IllegalArgumentException();

 // Will skip the nth - 1
 // 2 to n-1
 return IntStream.iterate(2, i -> i + 1).filter(PrimeCalculator::isPrime).skip(nth - 1).findFirst().getAsInt();
 }

The method nth(int) allows you to return the nth prime starting at 2, 3, 5....

Prime on Samarthya

Nth Prime

Explanation #

Explanation
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